Neurostimulation is a treatment method utilized for managing the disabilities associated with pain, movement disorders such as Parkinson's Disease (PD), dystonia, and essential tremor, and also a number of psychological disorders such as depression, mood, anxiety, addiction, and obsessive compulsive disorders.
At least some known neurostimulation systems are closed-loop spinal cord stimulation (SCS) systems based on neurological sensing systems. In at least some known systems, selecting parameters for SCS relies on a “guess-and-check” approach to find therapeutically effective parameter sets for chronic pain. For example, for traditional tonic (i.e., single pulse) stimulation waveforms, there are several parameters that can be independently tuned, including stimulation amplitude, pulse width, frequency, and contact configuration (e.g., the location of cathodes and anodes). Moreover, with the introduction of other stimulation waveforms, such as burst stimulation, there are even more parameters to tune, including inter-burst and intra-burst frequency. Finally, it is also desirable to determine which stimulation waveform (tonic, burst, etc.) generates the best response in each individual patient. In at least some known systems, however, the process for selecting stimulation parameters may not be well-defined for efficiently and rationally identifying parameters that facilitate generating optimal therapy.
In tonic SCS, stimulation parameters may be adjusted until there is paresthesia coverage of painful regions of the patient's body. The stimulation amplitude generally determines the extent of neuronal activation. Accordingly, in at least some known systems, amplitude is titrated between a perception threshold (i.e., a level at which the patient senses paresthesia) and a discomfort threshold (i.e., a level at which the patient experiences discomfort). The discomfort threshold may be, for example, 1.4 to 1.7 times the perception threshold. In addition, pulse width may be adjusted. Increasing pulse width generally leads to smaller differences in stimulation thresholds between large and small diameter fibers.
In high-frequency SCS, a tonic waveform may be applied at frequencies in the 2 to 10 kilohertz (kHz) range to generate pain relief with reduced paresthesia. For example, for 10 kHz stimulation, amplitude may be 0.5 to 5 milliamps (mA) and pulse width may be 30 microseconds (μs). Paresthesia mapping is not generally used for high-frequency SCS, and instead, a stimulation site is more consistent, with stimulation typically applied at C4-C5 for chronic pain of the upper limbs/hands, and at T8-T12 for the back and lower limbs.
For burst SCS, a waveform including packets of high-frequency pulses that are separated by a quiescent period is used. Burst SCS often results in paresthesia-free stimulation. Typical waveform parameters may be, for example, a 500-1000 hertz (Hz) intra-burst frequency, a 40 Hz intra-burst frequency, five pulses per burst, and 0.5-1 millisecond (ms) pulse width. The amplitude is typically subsensory (e.g., 90% of the paresthesia threshold), and may average around 3.4 mA.
In addition to selecting parameters, another difficulty in SCS programming arises when attempting to quantify patient pain. For example, patients may be asked to quantify their pain on a scale of 1 to 10, state their percentage pain relief compared to baseline, and/or identify body locations where pain relief and paresthesia are felt. The patient must continuously provide these subjective measures with each parameter adjustment, which can be time-consuming for both the patient and the programmer. Moreover, the reliability of these subjective pain measures is questionable.
Further, when delivering SCS stimulation, it may be desirable to extend the battery life of one or more components of an SCS system. As such, there is a need to identify SCS waveforms that provide substantially paresthesia-free stimulation while minimizing the amount of energy delivered.